Hydraulic pump or motor

ABSTRACT

The mechanism such as a motor or a pump comprises a cam ( 10 ) and a cylinder block ( 12 ) which has a plurality of cylinders ( 14 A,  14 B,  14 ) connected to communication orifices ( 34 A,  35 A;  34 B,  35 B) disposed in a communication face ( 18 ). The mechanism further comprises a fluid distributor ( 20 ) having a distribution face ( 22 ) which is provided with distribution orifices ( 31 A- 31 F,  32 A- 32 F) suitable for being connected to the feed or to the discharge. The communication orifices and the distribution orifices communicate with one another as the cylinder block and the distributor rotate relative to each other. At least certain cylinders ( 14 A,  14 B) are connected to at least two communication orifices ( 34 A,  35 A;  34 B;  35 B) spaced apart angularly (α) so that they communicate simultaneously with respective distribution orifices connected to the feed or to the discharge.

The present invention relates to a hydraulic mechanism such as a motoror a pump comprising a cam and a cylinder block suitable for rotatingrelative to each other about an axis of rotation, the cylinder blockhaving a plurality of cylinders connected via cylinder ducts tocommunication orifices disposed in a communication face of the cylinderblock, pistons slidably mounted in the cylinders being suitable forco-operating with the cam, the motor further comprising a fluiddistributor, constrained in rotation with the cam about the axis ofrotation, and having a distribution face which is provided withdistribution orifices comprising orifices suitable for being connectedto a feed duct and orifices suitable for being connected to a dischargeduct, said distribution face and said communication face facing eachother so as to put the communication orifices into communication withthe distribution orifices as the cylinder block and the distributorrotate relative to each other.

The speed of rotation of the rotor of such a hydraulic motor is limitedby the various types of head loss that are generated in the feed circuitof the motor and, in particular, by the head loss that is generated inthe motor itself. Among the various types of head loss, the head lossthat is generated in the distribution zone, i.e. where the communicationorifices meet the distribution orifices, is the largest.

As the rotor rotates, the communication orifices and the distributionorifices come progressively into register with one another. Thus, thecommunication cross-section over which the communication orifices andthe distribution orifices communicate varies. The slower the variationin communication cross-section as a function of the relativedisplacement of the communication and the distribution orifices, thelarger the head loss.

In order to limit that head loss, it has been proposed to increase thecross-section of the distribution orifices and of the communicationorifices. However, that solution has certain limitations because itrequires the distribution and the communication faces to have facingareas that are sufficiently large. In addition, providing orifices oflarge dimensions requires the motor to be provided with a bearingcapable of withstanding large forces. When a distribution orificeconnected to the fluid feed finds itself facing an uninterrupted zone ofthe communication face, it exerts a large force thereon.

It has also been proposed, as in FR-A-2 587 761, for example, to givesaid orifices a particular shape so that the cross-section ofcommunication between a communication orifice and a distribution orificeincreases very rapidly from the time at which the two orifices start tocommunicate.

That solution gives good results, but it still has certain limitations.

An object of the present invention is to improve the above-mentionedprior art further in order to facilitate communication between thedistribution ducts of the distributor and the cylinder ducts, bylimiting head loss in the distribution zone.

This object is achieved by the fact that at least certain cylinders areconnected to at least two communication orifices spaced apart angularlyso that, when a first communication orifice of such a cylindercommunicates with a first distribution orifice connected to the feedduct or to the discharge duct, a second communication orifice of thesame cylinder communicates with a second distribution orifice connectedto the same duct.

Compared with prior art motors in which each cylinder has a singlecommunication orifice in the communication face, and if it is consideredthat the dimensions of the communication orifice and of the distributionorifice remain unchanged, the cross-section available for fluid feed ordischarge for the cylinders of the motor of the invention, each of whichcylinders has two communication orifices, is doubled. Thus, the headloss is considerably reduced in the distribution zone and the speed ofrotation of the rotor of the motor can be increased.

Advantageously, with the cam having n cam lobes, the angular spacingbetween two communication orifices is substantially equal to a multipleof 360°/n, i.e. it is equal to a multiple of 360°/n, ignoringmanufacturing tolerances.

A hydraulic motor whose cam has n lobes and having a row of cylinderswhose pistons co-operate with said cam has, in the distribution face, nfeed distribution orifices, which are spaced apart by 360°/n and whichare suitable for being simultaneously connected to the feed duct, and ndischarge distribution orifices, also spaced apart by 360°/n andsuitable for being simultaneously connected to the discharge duct. Thefeed distribution orifices and the discharge distribution orifices areinterleaved. If each of the cam lobes has two ramps, respectively arising ramp and a falling ramp of equal angles, the angular spacingbetween a feed distribution orifice and the adjacent dischargedistribution orifice is equal to 360°/2n. Thus, in a motor of this type,choosing an angular spacing that is substantially equal to a multiple of360°/n between the two communication orifices of the same cylinder makesit possible to ensure that, as the rotor rotates, the two orifices areconnected in the same way, via the distribution orifices, to the feed orto the discharge.

In an advantageous configuration, at least certain cylinders areconnected to two communication orifices which are situated substantiallyor to a large extent within an area of the communication face that isdefined by the projection, onto said face and parallel to the axis ofrotation, of two generator lines of the cylinder in question that areopposite each other on a diametrical plane of said cylinder that isperpendicular to said axis.

In this configuration, the two communication orifices of the samecylinder are thus situated substantially or to a large extent within thespace occupied by said cylinder, as defined by the above-mentionedprojection. They are thus very close to each other, and they open outinto the cylinder merely via bores parallel to the axis of rotation,which facilitates machining the cylinder ducts that connect saidcommunication orifices to the cylinder in question. For example, it ispossible to choose to dispose the two communication orificessymmetrically about the axis of the cylinder and to implement thecylinder ducts of the cylinder in question in the form of two branchesthat are symmetrical about said axis.

This possibility of disposing the two communication orifices of the samecylinder substantially or to a large extent within the space occupied bythe cylinder exists in particular when the motor has a number of camlobes that is greater than the number of pistons, sufficient for theangular sector covered by the space occupied by the cylinder in theregion of the communication orifices to be at least equal to 360° C./n,where n represents the number of cam lobes.

In general, it can be advantageous for at least certain cylinders to beconnected to two communication orifices which are disposed symmetricallyabout a plane defined by the axis of the cylinder in question and by theaxis of rotation. This makes it possible for the communication orificesand the cylinder ducts to be implemented symmetrically, regardless ofwhether said communication orifices lie within the space occupied by acylinder.

In an advantageous embodiment, each cylinder is connected to twocommunication orifices.

The head loss is thus reduced for all of the cylinders of the motor.

In which case, advantageously, the angular spacing between the twocommunication orifices of the same cylinder is the same for all of thecylinders.

This configuration simplifies machining of the cylinder block.

Advantageously, with the cam having n cam lobes, said angular spacing isequal to 360°/n.

The two communication orifices of the same cylinder are thus broughtcloser together so as to limit the lengths of the cylinder ducts.

The invention applies to motors having pluralities of active operatingcubic capacities.

Thus, advantageously, the cam has a plurality of cam lobes, each ofwhich comprises a rising ramp and a falling ramp, each of which isassociated with a respective distribution orifice, a cam lobe beingconsidered to be active when the distribution orifice associated withits rising ramp is connected to the feed duct and when the distributionorifice associated with its falling ramp is connected to the dischargeduct, the hydraulic mechanism having a large active operating cubiccapacity in which all of the cam lobes are active, and a small activeoperating capacity in which only some of the cam lobes are active; thecam lobes that are active in the small active operating cubic capacityare disposed asymmetrically.

Thus, regardless of whether the motor is operating in small cubiccapacity mode or in large cubic capacity mode, the two communicationorifices of a cylinder whose piston co-operates at a given instant withan active cam lobe, are connected to the same pressure by beingconnected to distribution orifices that are either at the feed pressureor at the discharge pressure.

The invention will be well understood and its advantages will appearmore clearly on reading the following detailed description ofembodiments given by way of non-limiting example.

The description is given with reference to the accompanying drawings, inwhich:

FIG. 1 is an axial section view through a hydraulic motor of theinvention;

FIG. 2 is a section view on line II-II, taken perpendicularly to theaxis of rotation and in the communication face of the cylinder block ofa hydraulic motor of the invention;

FIGS. 3 and 4 are section views respectively on line III-III and on lineIV-IV of FIG. 2;

FIG. 5 is a view analogous to the FIG. 2 view, for a variant embodiment;

FIG. 6 is a view analogous to the FIG. 2 view, for another variant; and

FIG. 7 is a fragmentary view, taken on the same section as FIG. 2,showing yet another variant.

FIG. 1 shows a hydraulic motor comprising a stationary casing in threeportions 2A, 2B, and 2C, assembled together by bolts 3.

Naturally, the invention is not limited to hydraulic motors havingstationary casings, but rather it also applies to hydraulic motorshaving rotary casings and that are well known to the person skilled inthe art.

The portion 2C of the casing is closed axially by a radial plate 2D alsofastened by bolts. An undulating reaction cam 10 is formed on theportion 2B of the casing.

The motor comprises a cylinder block 12 which is mounted to rotate aboutan axis of rotation A relative to the cam 10, and which is made up of aplurality of radial cylinders 14 that are suitable for being fed withfluid under pressure and that slidably receive the radial pistons 16.

The cylinder block 12 drives a shaft 5 that co-operates with it viafluting 7. Said shaft carries an outlet flange 9.

The motor further comprises an internal fluid distributor 20 which isconstrained to rotate with the casing about the axis A. Distributiongrooves, respectively a first groove 15, a second groove 17, and a thirdgroove 19, are formed between the distributor 20 and the internal axialface of the portion 2C of the casing. The distribution ducts of thedistributor 20 are disposed in a first group of ducts which, like theduct 15A, are all connected to the groove 15, in a second group of ducts(not shown) which are connected to the groove 17, and in a third groupof ducts which, like the duct 19A, are connected to the groove 19. Thefirst groove 15 is connected to a first main duct P1 which is thusconnected to all of the distribution orifices of the distribution ductsof the first group, such as orifice 31 of duct 15A. The third groove 19is connected to a second main duct P2 which is thus connected to all ofthe distribution orifices of the ducts of the third group, such asorifice 32 of duct 19A.

Depending on the direction of rotation of the motor, the main ducts P1and P2 are respectively a fluid discharge duct or a fluid feed duct, orvice versa.

The distribution ducts open out in a distribution face 22 of thedistributor 20, which face bears against a communication face 18. Eachcylinder 14 has two cylinder ducts 34′A, 35′A which open out in thecommunication face 18 so that, while the cylinder block and the cam arerotating relative to each other, the cylinder ducts are alternately incommunication with the distribution ducts of the various groups.

The motor of FIG. 1 further comprises a cubic-capacity selector devicewhich, in this example, is provided with a bore 40 which extends axiallyin the portion 2C of the casing, and in which an axially movableselector slide 42 is disposed. The bore 40 is provided with threecommunication ports, respectively 44, 46, and 48, which are connected torespective ones of the grooves 15, 17, and 19, via link ducts. The slide42 is mounted to move between two end positions inside the bore 40, inwhich end positions it puts the ports 44 and 46 or the ports 46 and 48into communication via its groove 43.

The section of FIG. 1 is taken in the communication face 18 of thecylinder block, which face contains the communication orifices of thecylinder ducts which are each connected to a respective cylinder 14. Inorder to make the present description clearer, the positions of thedistribution orifices are also indicated in FIG. 2, even though they donot lie in the section plane.

In addition, although they are not situated in the section plane, thepistons and the cylinders are shown in uninterrupted lines for reasonsof simplicity.

As can be seen in FIG. 1, the distribution face 22 and the communicationface 18 are disposed facing each other. Since the distribution and thecommunication orifices are situated at the same distance from the axisA, it is possible to put said communication orifices and saiddistribution orifices into communication as the cylinder block 12 andthe distributor 20 rotate relative to each other.

FIGS. 1 and 2 show a motor having radial pistons and “plane”distribution. The communication and the distribution faces areperpendicular to the axis of rotation, and both of them are plane. Insuch a case, said communication and distribution faces are held inabutment against each other, with the distributor being urged intoabutment with the cylinder block. However, the invention applies toother types of motor, e.g. to motors having cylindrical distribution.

As can be seen in FIG. 2, the cam 10 comprises a plurality of cam lobes,referenced 9A to 9F. Each lobe comprises a rising ramp respectivelyreferenced 91A to 91F, and a falling ramp respectively referenced 92A to92F. This means that, as the cylinder block rotates in the direction Rrelative to the cam, those pistons 15 whose wheels 16A co-operate withrising ramps move radially outwards, while those whose wheels co-operatewith falling ramps move radially inwards by retracting into theircylinders. Each ramp of a cam lobe is associated with a distributionorifice. Thus, the distribution orifices 31A to 31F are associated withrespective ones of the rising ramps 91A to 91F, while the distributionorifices 32A to 32F are associated with respective ones of the fallingramps 92A to 92F. Although the cam is made in one piece, and for reasonsof clarity, the rising and the falling ramps are shown with differentshading.

In the example shown, each cylinder is connected to the communicationface 18 via two communication orifices. Thus, the cylinder 14A whosepiston 16 co-operates with the rising ramp 91A of the cam lobe 9A isconnected to the communication face 18 via a first communication orifice34A, and also via a second communication orifice 35A. Similarly, thecylinder 14B whose piston co-operates with the rising ramp 91B of thecam lobe 9B is connected to the communication face via a firstcommunication orifice 34B and via a second communication orifice 35B.

On looking at the cylinder 14A, it can be seen that its communicationorifice 34A communicates with the distribution orifice 31A and that, atthe same time, its communication orifice 35A communicates with thedistribution orifice 31B. The two distribution orifices are connected tothe same pressure; in this example, they are both connected to the fluidfeed because they are associated with rising ramps, respectively 91A and91B. It can also be seen that the cross-section of communication betweenthe orifice 34A and the orifice 31A, and the cross-section ofcommunication between the orifice 35A and the orifice 31B are the same.Thus, the cylinder 14A is simultaneously fed with fluid coming from thedistribution orifices 31A and 31B and passing through the communicationorifices 34A and 35A while the piston 16 is rising on the ramp 91A, fromits low end 91′A to its high end 91″A. The communication between theorifice 34A and the orifice 31A, in the same way as the communicationbetween the orifice 35A and the orifice 31B, starts when the wheel 16Aof the piston comes into contact with the bottom end 91′A, and ceaseswhen said wheel comes into contact with the high end 91″A.

In this example, each cylinder is provided with two communicationorifices, and the above explanations apply for all of the cylinders. Inorder to avoid cluttering the drawing, numerical references are givenonly to the communication orifices 34A and 35A that are associated withthe cylinder 14A, and to the communication orifices 34B and 35B that areassociated with the cylinder 14B. These explanations naturally alsoapply for co-operation between a piston and a falling ramp and forcommunication between the communication orifices of the cylinder of saidpiston and respective ones of two distribution orifices both connectedto the discharge duct.

The angular spacing α between the two communication orifices 34A and 35Aof the cylinder 14A is chosen so that, while the cylinder block and thecam are rotating relative to each other, the communication between saidorifices and respective ones of two distribution orifices opens at thesame time and closes at the same time.

The angular position of the distribution orifices relative to the lobesof the cam is fixed since the distributor and the cam are constrained torotate with each other. The distribution orifices connected to twoconsecutive rising ramps or to two consecutive falling ramps are spacedapart by a value equal to 360°/n, where n represents the number of camlobes. That is why the angular spacing α is equal to a multiple of360°/n.

This condition is necessary so that communication between the twocommunication orifices of the same cylinder and the respective ones ofthe two distribution orifices associated with the lobes of the same camis strictly synchronized.

For each cylinder 14 of FIG. 2, one of the communication orificesintersects a plane defined by the axis of the cylinder in question andby the axis of rotation. Thus, the orifice 34A is centered on the axisA14 of the cylinder 14A. A configuration of this type is conventionalfor prior art motors having only one communication orifice per cylinder.Conversely, the second communication orifice 35A of the cylinder isspaced apart from the axis A14.

FIG. 3 shows the configuration of the cylinder duct 34′A that connectsthe communication orifice 34A to the cylinder 14A. This duct isadvantageously formed in a manner such as to have a shape that is assimple as possible, and, for example, it comprises a radial segment 34″Awhich extends from the end-wall of the cylinder towards the axis ofrotation A, and an axial segment 34″′A which opens out at thecommunication orifice 34A.

FIG. 4 shows the shape of the cylinder duct 35′A connecting the samecylinder 14A to its second communication orifice 35A. This duct 35′A hasa first segment 35″A which is disposed on a slant as seen in a planeparallel to the plane of FIG. 2 so as to cover the angular spacingbetween the orifices 34A and 35A, and which is connected to a secondsegment 35′″A which is axial and which opens out at the communicationorifice 35A.

It can be seen that the axial segments 34′A and 35′A do not have thesame length, so that the segments 34″A and 35″A do not intersect eachother. In order to simplify FIG. 2, the only cylinder ducts whoseposition is indicated are the ducts 34′A and 35′A.

In FIG. 5, the same references as in FIG. 2 are used.

Each cylinder is provided with two communication orifices, designated byreferences 34A and 35A for the cylinder 14A. Unlike the configuration inFIG. 2, neither of these two orifices is situated on the axis of itscylinder. In FIG. 5, the orifice 34A is slightly offset relative to theorifice 34A of FIG. 2 in the opposite direction to the direction R.However, the angular spacing a between the two orifices 34A and 35A ofthe same cylinder is unchanged, and is equal to 360°/n, where nrepresents the number of cam lobes.

The distribution orifices are also slightly offset relative to theorifices of FIG. 2 in the opposite direction to the direction R. What isimportant for ensuring that the motor operates properly is that thecommunication between a communication orifice of a cylinder (e.g.orifice 34A) and a distribution orifice connected to the fluid feed(orifice 31A in this example) opens when, as the cylinder block rotatesin the direction R relative to the cam, the piston 16 of the cylinder14A in question co-operates with the low end 91′A of the rising ramp 91Aof the cam lobe with which the distribution orifice in question isassociated, and closes when the same piston co-operates with the highend 91″A of said ramp. The angular offset that exists between thecommunication orifices of FIGS. 2 and 5 is thus the same as the angularoffset that exists between the distribution orifices of said Figures.

FIG. 6 is described below. In FIG. 6, which uses the same references asFIGS. 2 and 5, the two communication orifices of the same cylinder aredisposed symmetrically about a plane defined by the axis of the cylinderin question and by the axis of rotation. Thus, the orifices 34A and 35Aof the cylinder 14A are disposed symmetrically about the plane definedby the axis A and by the axis A14 of the cylinder 14A.

It can be understood that the angular spacing αA between a radiusstarting from the axis A and passing through the center of the orifice34A, and a projection of the axis A14 on the communication face 18 isequal to the angular spacing αB between said projection of the axis A14on the communication face, and a radius passing through the center ofthe orifice 35A. The sum of said angular spaces is equal to the angularspacing α, which is itself equal to twice 360°/n, where n is the numberof cam lobes.

In the example shown in FIG. 6, the distribution orifices are offsetrelative to FIG. 2 to an even further extent than in FIG. 5, to theextent where the distribution orifices associated with one of the rampsof a cam lobe do not even lie within the angular sector covered by saidramp. Thus, the orifice 31A is situated in an angular sector covered bythe ramp 91F, while the orifice 32A lies within the space covered by theramp 92F, but it is when the communication orifice 34A communicates withthe orifice 31A (and when, simultaneously, the communication orifice 35Acommunicates with the distribution orifice 31C) that the piston which isdisposed in the cylinder 14A co-operates with the ramp 91A.

Under certain conditions, the two communication orifices of the samecylinder being symmetrical about the projection of the axis of thecylinder on the communication face facilitates machining the cylinderducts.

As indicated with reference to FIGS. 3 and 4, it is possible to makeprovision so that each of the cylinder ducts has an axial segment and,so that, for the two cylinder ducts of the same cylinder, the non-axialsegments of said ducts do not lie in the same plane, in order to avoidintersections, e.g. between the cylinder duct 14A that opens out intothe communication orifice 35A and the cylinder duct of the cylinder 14Bthat opens out into the communication orifice 34B.

Between the FIGS. 2, 5, and 6, neither the number of cam lobes nor thenumber of cylinders varies. In this example, the motor has a number ofcylinders that is higher than the number of cam lobes.

The motor of FIG. 7 is slightly different and references increased by100 are used to describe it. In this figure, it can be seen that theangular spacing covered by a cam lobe such as 109A or 109B, which is360°/n, where n represents that number of cam lobes, is less than theangular spacing α114 as measured from the end-wall of a cylinder 114 andcovered by said cylinder.

In FIG. 7, the wheel 116A of the piston 116 co-operates with the middleportion of the rising ramp 191A of the cam lobe 109A, and communicationbetween the communication orifices 134A and 135A of the cylinder 114A inwhich the piston moves and the distribution orifices 131A and 131B ismaximized. The two distribution orifices 131A and 131B are twodistribution orifices associated respectively with the rising ramps 191Aand 191B of two consecutive cam lobes 109A and 109B. Unlike theconfigurations in the preceding figures, the number of cam lobes issufficient so that the angular space a covered by a cam lobe is smallerthan the angular space α114 covered by a cylinder. Thus, while beingspaced apart at an angle α equal to 360°/n where n is the number of camlobes, the two communication orifices 134A and 135A of the same cylinder114A can substantially lie within the space occupied by said cylinder.In other words, the two communication orifices are situated within anarea of the communication face 118 that is defined by the projectiononto said face and parallel to the axis of rotation A of two generatorlines G1 and G2 of the cylinder 114A that are opposite each other on adiametrical plane of said cylinder that is perpendicular to the axis A.

This configuration, which is possible only when the ratio between thenumber of cam lobes and the number of cylinders is sufficiently high,makes it possible to simplify machining of the cylinder ducts that openout into the two communication orifices of the same cylinder, said ductsnot intersecting the cylinder ducts of another cylinder.

It can also be noted in FIG. 7 that the communication orifices are of aparticular shape, with their sides being concave. This configuration,which is known per se from Document FR-A-2 587 761 makes it possible toensure that, when a communication orifice starts to communicate with adistribution orifice, the cross-section of communication between the twoorifices varies very quickly as the cylinder block and the cam rotaterelative to each other. This limits head loss.

Thus, the invention can be used jointly with other particularconfigurations that are already known for limiting head loss.

It can also be used with communication orifices of any shape, e.g.circular, that might be easier to form.

The motor shown in the figures can have two active operating cubiccapacities.

Thus, when the motor is in the large active cubic capacity, all of thecam lobes are active, i.e. all of the distribution orifices associatedwith the rising ramps are connected to the feed duct and all of thedistribution orifices associated with the falling ramps are connected tothe discharge duct. Thus, as the cylinder block and the cam rotaterelative to each other, the communication orifices of a cylinder arealternately connected to the high pressure and to the low pressure.

In certain motors, the cubic capacity is selected by cams. This meansthat, in the small active operating cubic capacity, certain cam lobesare active. For example, if FIG. 6 is considered, it is possible to makeprovision for only the cam lobes 9A, 9C and 9E to be active in the smalloperating cubic capacity, the distribution orifices 32A, 32C and 32Eassociated with their respective falling ramps being respectivelyconnected to the fluid feed and to the fluid discharge. In the smallactive cubic capacity, the other cam lobes are inactive, which meansthat, for example for the lobe 9B, the distribution orifices 31B and 32Bare connected to the same pressure which, depending on thecircumstances, can be the fluid discharge pressure, an is auxiliarypressure, or even the feed pressure.

It can be observed that the lobes 9A, 9C, and 9E which are active in thesmall active operating cubic capacity are disposed asymmetrically. Forreasons of clarity of the drawing, the shading of the cam lobes that areactive in the small cubic capacity is uninterrupted, while the shadingof the cam lobes that are inactive is dashed.

In this case, if k is the number of cam lobes that are active in thesmall active operating cubic capacity, then the angular spacing betweenthe two communication ducts of the same cylinder must be equal to amultiple of 360°/k. As can be seen in FIG. 6, in order for motor tooperate in the small active cubic capacity, it must be possible for thefirst communication duct 34A of the cylinder 14A to communicate with adistribution orifice 31A associated with the ramp 91A of the cam lobe 9Awith which the piston that is disposed in the cylinder in questionco-operates, and, at the same time, for the second communication duct35A of the same cylinder to co-operate with another communicationorifice 31C which is also associated with the rising ramp of an activecam lobe (the ramp 91C in this example).

In FIG. 6, the motor has six cam lobes, three of which are active in thesmall operating cubic capacity, and the angular spacing α between thetwo communication orifices of the same cylinder is equal to 120°.Naturally, although it can be advantageous to dispose the twocommunication orifices of the same cylinder symmetrically about a planecontaining the axis of said cylinder and containing the axis A ofrotation of the motor, the choice of such a configuration is notnecessarily related to the possibility of implementing the invention ina motor having at least two active operating cubic capacities, and inwhich the cubic capacities are selected by the cams.

In addition, the invention naturally applies to motors in which cubiccapacity is selected directly by the cylinders. It also applies tomotors or pumps having axial pistons and cams presenting a plurality oflobes.

Naturally, when the cylinder ducts are long and of complex shape, andtherefore difficult to machine, it is possible to make a communicationinterface part which can have duct segments that are machined or cast.

1-9. (canceled)
 10. A hydraulic mechanism such as a motor or a pumpcomprising a cam and a cylinder block suitable for rotating relative toeach other about an axis of rotation, the cylinder block having aplurality of cylinders connected via cylinder ducts to communicationorifices disposed in a communication face of the cylinder block, pistonsslidably mounted in the cylinders being suitable for co-operating withthe cam, the motor further comprising a fluid distributor, constrainedin rotation with the cam about the axis of rotation, and having adistribution face which is provided with distribution orificescomprising orifices suitable for being connected to a feed duct andorifices suitable for being connected to a discharge duct, saiddistribution face and said communication face facing each other so as toput the communication orifices into communication with the distributionorifices as the cylinder block and the distributor rotate relative toeach other, at least certain cylinders being connected to at least twocommunication orifices spaced apart angularly so that, when a firstcommunication orifice of such a cylinder communicates with a firstdistribution orifice connected to one of the feed duct and the dischargeduct, a second communication orifice of the same cylinder communicateswith a second distribution orifice connected to said one of the feedduct and the discharge duct.
 11. A hydraulic mechanism according toclaim 10, wherein the cam has n cam lobes, n being an integer and anangular spacing between two communication orifices of the same cylinderis substantially equal to a multiple of 360°/n.
 12. A hydraulicmechanism according to claim 10, wherein at least one cylinder isconnected to two communication orifices which are situated in an area ofthe communication face that is defined by the projection, onto said faceand parallel to the axis of rotation, of two generator lines of thecylinder in question that are opposite each other on a diametrical planeof said cylinder that is perpendicular to said axis.
 13. A hydraulicmechanism according to claim 10, wherein at least one cylinder isconnected to two communication orifices which are disposed symmetricallyabout a plane defined by an axis of the cylinder in question and by theaxis of rotation.
 14. A hydraulic mechanism according to claim 10,wherein at least one cylinder is connected to two communicationorifices, one of which intersects a plane defined by an axis of acylinder in question and by the axis of rotation.
 15. A hydraulicmechanism according to claim 10, wherein each cylinder is connected totwo communication orifices.
 16. A hydraulic mechanism according to claim15, wherein an angular spacing between the two communication orifices ofa cylinder is the same for all of the cylinders.
 17. A hydraulicmechanism according to claim 16, wherein the cam has n cam lobes, nbeing an integer and the angular spacing is equal to 360°/n.
 18. Ahydraulic mechanism according to claim 10, wherein the cam has aplurality of cam lobes, each of which comprises a rising ramp and afalling ramp, each of which is associated with a respective distributionorifice, a cam lobe being considered to be active when the distributionorifice associated with the rising ramp of said cam lobe is connected tothe feed duct and when the distribution orifice associated with thefalling ramp of said cam lobe is connected to the discharge duct, thehydraulic mechanism having a large active operating cubic capacity inwhich all of the cam lobes are active, and a small active operatingcapacity in which only some of the cam lobes are active, and wherein thecam lobes that are active in the small active operating cubic capacityare disposed asymmetrically.